Sputtering target structure

ABSTRACT

To provide a sputtering target structure which has good machinability and thermal conductivity and has good wettability with soldering materials, which is inexpensive and can be used repeatedly for a long period of time, and which is free from problems of cracking and peeling of the sputtering target therein, a sputtering target structure is formed by bonding a sputtering target and a backing plate. The backing plate is formed of a material that has the difference in the linear expansion coefficient between it and the sputtering target material of at most 2×10 −6 /K, and a copper plate having a thickness of from 0.3 to 1.5 mm is disposed on at lest one face of the backing plate.

TECHNICAL FIELD

The present invention relates to a sputtering target structure for usein a sputtering step in production of a thin film for hard coating ordecorative coating of flat panel displays (hereinafter referred to as“FPD”) such as liquid-crystal displays, plasma displays, etc.

BACKGROUND ART

Thin film formation through sputtering comprises introducing a rare gassuch as argon into a vacuum chamber, applying a negative voltage to thesputtering target in the chamber to cause glow discharge therein, makingthe thus-formed plasma cations collide with the sputtering target, anddepositing the thus-released, sputtering target-constitutive atom on thesubstrate disposed opposite to the target.

Typically, the sputtering target includes aluminium, aluminium alloy,high-melting-point metal (e.g., tungsten, molybdenum, titanium) and itsalloy, high-melting-point silicide (e.g., molybdenum silicide, tungstensilicide); and recently, a sintered ITO (indium-tin-oxide) body hasbecome used for it.

A backing plate functions as a support, and further functions as acooling medium for removing heat from the sputtering target thatgenerates heat therein during sputtering. Accordingly, the backing plategenerally has a cooling mechanism inside it.

For the backing plate, used are oxygen-free copper, copper alloy,aluminium alloy, stainless steel, titanium alloy, etc. Of those, acopper backing plate is favorably used, as its thermal conductivity isgood. However, its linear expansion coefficient is 17×10⁻⁶/K and islarge, and this is problematic in that its deformation is great owing toits elongation in repeated use and, after used a few times, it could nomore be reused.

The sputtering target for use in the above-mentioned sputtering step isgenerally used in the form of a structure thereof soldered to a backingplate with a low-melting-point soldering material.

In the sputtering step, when the sputtering target structure is heatedhigh owing to the collision of plasma cations therewith and when thereis a great difference in the linear expansion coefficient between thesputtering target and the backing plate constituting it, then thesputtering target structure may deform like a bimetal. The deformationmay occur also in producing the sputtering target structure.

The deformation produces some problems in that the sputtering target maycrack, the soldering material may fuse and the soldered part may peel.

Accordingly, a sputtering target structure is desired, which does notcause bimetal deformation even when exposed to high temperatures insputtering and which is therefore free from the problems of cracking andpeeling of the sputtering target thereof.

Recently, molybdenum and titanium have become used as a sputteringtarget material, and the linear expansion coefficient of these metalsgreatly differs from the linear expansion coefficient of copper that isfavorably used for a backing plate material. Therefore, the requirementfor the sputtering target structure free from the above-mentionedproblems is great.

For obtaining the sputtering target structure free from theabove-mentioned problems, various proposals have heretofore been made.

For example, investigations of soldering materials and soldering methodshave produced a method comprising disposing a tin alloy sheet or thelike between a sputtering target and a cooling plate (backing plate),putting an indium alloy between the sheet and the sputtering target andbetween the sheet and the cooling plate, and heat-sealing them (PatentReference 1); a method comprising subjecting a sputtering target forplating to a pretreatment such as plating or vapor deposition thereonand inserting a buffer material between the sputtering target and acooling plate (backing plate) (Patent Reference 2); a method comprisinginserting an insert material between a sputtering target and a coolingplate (backing plate) (Patent Reference 3); a method comprisinginserting a heat-conductive adhesive between a sputtering target and abacking plate and adhering them with a low-melting-point metal disposedbetween the adhesive and the sputtering target and/or the backing plate(Patent Reference 4).

These methods are to attain the effect through modification of theconstitution of the thin solder material layer between the sputteringtarget and the backing plate, and they could hardly attain the intendedeffect. In these methods, in addition, the minus effect of thermalconductivity depression owing to the disposition of various materialsbetween the sputtering target and the backing plate cannot be bypassed.Further, the use of indium is problematic in point of its cost.

On the other hand, a backing plate investigation has proposed a methodof forming a three-layered backing plate structure ofmolybdenum-titanium-molybdenum, as is disclosed in Patent Reference 5.This is for making the linear expansion coefficient of the backing platethe same as that of the sputtering target to be combined with it.

Patent Reference 6 discloses a backing plate formed of a compositematerial of molybdenum and copper.

Patent Reference 7 proposes production of a backing plate from acomposite material of aluminium or aluminium alloy with ceramic.

However, these materials have poor machinability, and are hardlyapplicable to large-sized products for FPD for which, in particular, thethermal expansion difference between the sputtering target and thebacking plate is especially problematic.

Patent Reference 8 proposes a backing plate comprising titanium.However, its thermal conductivity is extremely low and this isunfavorable to a structure of a sputtering target and a backing plateequipped with a cooling mechanism.

Further, Patent Reference 9 proposes a technique of providing grooves onthe surface of a backing plate to be bonded to a sputtering target. Inthis, the grooves are to absorb thermal deformation, but on the otherhand, this is problematic in that its thermal conductivity depression isinevitable.

-   Patent Reference 1: JP-A 61-250167-   Patent Reference 2: JP-A 5-25620-   Patent Reference 3: JP-A 4-365857-   Patent Reference 4: JP-A 2000-160334-   Patent Reference 5: JP-A 8-246144-   Patent Reference 6: JP-A 62-67168-   Patent Reference 7: JP-A 2002-161361-   Patent Reference 8: JP-A 6-293963-   Patent Reference 9: JP-A 2-43362

DISCLOSURE OF THE INVENTION Problems that the Invention is to Solve

Accordingly, an object of the invention is to provide a puttering targetstructure which has good machinability and thermal conductivity and hasgood wettability with soldering materials, which is inexpensive and canbe used repeatedly for a long period of time, and which is free fromproblems of cracking and peeling of the sputtering target therein.

Means for Solving the Problems

For attaining the above-mentioned object, we, the present inventors haveassiduously studied the constitution of a sputtering target structureand the materials of the members constituting it, and, as a result, havefound that use of a composite material of aluminium with a substancehaving a small linear expansion coefficient for the main material of abacking plate may solve the problems, and on the basis of this finding,we have further studied and have finally completed the presentinvention.

Accordingly, the invention provides a sputtering target structure formedby bonding a sputtering target and a backing plate, wherein the backingplate is formed of a material that has a linear expansion coefficientdifferent from that of the sputtering target material by at most2×10⁻⁶/K, and a copper plate having a thickness of from 0.3 to 1.5 mm isdisposed on at lest one face of the backing plate.

Preferably in the sputtering target structure of the invention, thematerial to constitute the backing plate is a composite material thatcomprises aluminium or aluminium alloy as the matrix and, asincorporated therein, one or more granular or fibrous reinforcingmaterials selected from the group consisting of carbon, silicon carbide,alumina, silicon nitride, mullite and aluminium borate, and the materialhas a linear expansion coefficient of from 3.5 to 17×10⁻⁶/K.

Also preferably in the sputtering target structure of the invention, thesputtering target and the backing plate are bonded together with indium,tin or their alloy.

Also preferably in the sputtering target structure of the invention, thebacking plate has a cooling channel inside it and the inner coolingchannel is a copper or stainless steel pipe.

EFFECT OF THE INVENTION

In the sputtering target structure of the invention, the difference inthe linear expansion coefficient between the sputtering target and thebacking plate is small; and therefore, even at high temperatures, thestructure does not warp and the sputtering target and the backing platetherein do not peel from each other, and the structure enables stablesputtering. In addition, the sputtering target structure of theinvention is inexpensive and can be used repeatedly many times, and itseconomical advantages are great.

DESCRIPTION OF THE DRAWINGS

FIG. 1. It is a schematic view of a sputtering target structure.

FIG. 2. It is a schematic view of a disposition of cooling pipes in aniron chamber.

FIG. 3. It is a schematic view of a shaped article formed by sintering areinforcing material.

FIG. 4. It is a schematic view of a shaped article with a copper platedisposed on both faces thereof.

FIG. 5. It is a cross-sectional view of a high-pressure casting device.

FIG. 6. It is a schematic view of a backing plate.

DESCRIPTION OF REFERENCE NUMERALS

-   1 Sputtering target structure-   2 Sputtering target-   3 Backing plate-   30 Shaped article of reinforcing material-   301 Carbon fiber-   302 Aluminium melt-   303 Composite material of aluminium and carbon fiber-   31 Stainless steel pipe for cooling-   32 Copper plate-   4 Iron chamber-   41 Space-   5 High-pressure casting mold

BEST MODE FOR CARRYING OUT THE INVENTION

The sputtering target structure of the invention comprises a sputteringtarget and a backing plate bonded to each other.

Not specifically defined, the sputtering target may be formed of anyknown sputtering target material, but preferably has a linear expansioncoefficient of from 3.5 to 17×10⁻⁶/K.

The size of the sputtering target is not also specifically defined.

Not specifically defined, the material to constitute the backing platein the invention may be any one that has the difference in the linearexpansion coefficient between it and the sputtering target material ofat most ±2×10⁻⁶/K.

In the invention, the material to form the backing plate is preferably acomposite material that comprises aluminium or aluminium alloy as thematrix and, as incorporated therein, one or more granular or fibrousreinforcing materials selected from the group consisting of carbon,silicon carbide, alumina, silicon nitride, mullite and aluminium borate,and the material has a linear expansion coefficient of from 3.5 to17×10⁻⁶/K.

Formation of the backing plate from the above-mentioned material bettersthe machinability of the formed backing plate, and facilitates theprocess of forming holes in the plate through which the plate is fittedin a vacuum chamber.

In case where a hardly-machinable material such as silicon carbide isused as the reinforcing material, the composite material containing itmay be hardly machined, and therefore, it is desirable that the materialis used in a part of the structure that does not require machining.

In the invention, the blend ratio of the reinforcing material toconstitute the composite material may be suitably selected so that theresulting composite material may have the above-mentioned linearexpansion coefficient.

For example, when molybdenum having a linear expansion coefficient of5.1×10⁻⁶/K is used as a sputtering target material, then the compositematerial to be combined with it may comprise a JIS-AC3A alloy and carbonfibers, having a linear expansion coefficient of from 4 to 5.5×10⁻⁶/K.

When a titanium alloy having a linear expansion coefficient of 9×10⁻⁶/Kis used as a sputtering target material, then the composite material tobe combined with it may comprise a JIS-A1050 alloy containing siliconcarbide powder in an amount of 65% by volume and carbon fibers andhaving a linear expansion coefficient of from 8.5 to 9.5×10⁻⁶/K.

Other combination examples of various sputtering target materials andcomposite materials suitable to the sputtering target materials areshown in Table 1.

TABLE 1 Target Material Composite Material for Backing Plate LinearLinear Expansion Expansion Coefficient (*) Coefficient Metal (×10⁻⁶/K)Composition (vol. %) (×10⁻⁶/K) copper 16.6 aluminum 80-alumina 20 17-18titanium 8.5 aluminum 35- 8-9 silicon carbide 65 chromium 6 aluminum 25-6-7 silicon carbide 75 molybdenum 5 aluminum 70- 5-6 carbon fibers 30aluminum 100 25 (*) From “Physical Dictionary” by Baifu-kan.

The backing plate to constitute the sputtering target structure of theinvention has a copper plate disposed on its side.

The copper plate may be disposed on at least one face of the backingplate, but is preferably disposed on both faces, or that is, on thefront and the back faces of the backing plate for more effectivelypreventing the deformation of the backing plate owing to its bimetalaction.

The thickness of the copper plate is from 0.3 to 1.5 mm, preferably from0.5 to 1.2 mm. When the thickness is more than 1.5 mm, then it isunfavorable since the thermal expansion of the backing plate may belarge. On the contrary, when the thickness is less than 0.3 mm, then itis also unfavorable since the workability of the backing plate may bepoor in forming it.

Copper has better solder-wettability and thermal conductivity thanaluminium, and therefore, when a copper plate is disposed on both facesof the backing plate, then the backing plate may realize excellentsolder-wettability and thermal conductivity.

Not specifically defined, a copper plate may be disposed on the side ofthe backing plate in any desired manner. For example, according to themethod mentioned below, a copper plate may be bonded to the backingplate while the backing plate is cast.

In the invention, a cooling channel is disposed inside the backingplate.

Provision of the cooling channel inhibits the expansion of the backingplate by the heat from the sputtering target to be sputtered, andprevents the low-melting-point solder material from melting, thereforepreventing the sputtering target from peeling from the backing plate.

Regarding its material, the cooling channel is preferably formed ofstainless steel or copper.

For forming the cooling channel inside the backing plate, it isdesirable that the composite material for the backing plate is cast andsolidified into the plate, while integrated with the pipes formed of thematerial for the channel to be inside the plate.

Not specifically defined, the cross-sectional profile of the pipe forthe cooling channel may be circular, angular or oval.

For producing the backing plate, concretely, the following method may beemployed.

For example, a reinforcing material is filled into the space of an ironmold while pipes to be a cooling channel are put in the mold. The methodfor filling the reinforcing material is not specifically defined. Areinforcing material may be cast into the mold in the form of a silicaslurry or the like.

Next, the mold with the cooling pipes and slurry therein is subjected toheat treatment, whereby the slurry is fired and the sintered article ofthe reinforcing material is taken out of the mold.

A copper plate is fitted to the sintered article in any desired manner,then this is put in a high-pressure casting mold, and an aluminium meltis cast into the mold and solidified under high pressure.

The sputtering target structure of the invention may be produced bybonding a sputtering target to the backing plate thus produced in themanner as above.

Bonding the sputtering target to the backing plate may be effected bythe use of any known solder material, for which preferred is indium, tinor their alloy.

In the sputtering target structure of the invention, such an inexpensivetin alloy may produce a sufficient bonding force, and the structure istherefore economical and advantageous.

EXAMPLES

The invention is described in more detail with reference to thefollowing Examples, to which, however, the invention should not belimited.

Example 1

This is described with reference to the drawings.

Five stainless steel pipes 31 (outer diameter 15 mm, pipe wall thickness1 mm) were aligned in an iron chamber 4 having a length of 2,000 mm awidth of 400 mm and a depth of 40 mm, at regular intervals in the crossdirection of the chamber (the distance between the side of the chamberand the outermost pipe in the cross direction was 30 mm), in such amanner that the distance from the bottom surface or the top surface ofthe chamber to the pipe could be the same (FIG. 2). The space 41 wasfilled with a reinforcing material, or that is, carbon fibers 301 havinga diameter of 8 μm and a length of 10 mm so that the volume percentageof the carbon fibers in the space 41 could be 30%. Next, 5% by weight ofsilica sol was cast into it, dried at 100° C., then fired in nitrogen at700° C., and thereafter the iron chamber 4 was removed to obtain acarbon fiber shaped article 30 with the stainless steel pipes 31 builttherein (FIG. 3).

A copper plate 32 having a thickness of 1 mm, a length of 2,000 mm and awidth of 400 mm was disposed on both faces of the shaped article 30(FIG. 4), and put in a high-pressure casting mold 5 (FIG. 5). Analuminium melt 302 at 800° C. was cast into the mold 5 and solidifiedunder high pressure at a pressure of 55 MPa. After thus completelysolidified, the cast product was taken out, the excess aluminium partwas removed, and a baking plate 3 was thus obtained, comprising acomposite material 303 of aluminium 302 and carbon fibers 301,containing stainless pipes 31 built therein, and having copper plate 32disposed on both surfaces thereof (FIG. 6).

The linear expansion coefficient of the backing plate 3 was 5.6×10⁻⁶/K.

Next, onto the copper plate 32 disposed on one side of the backing plate3, a solder tin was applied at 280° C. Next, a molybdenum sputteringtarget 2 (having a thickness of 15 mm, a length of 1,900 mm and a widthof 350 mm) was bonded to it to complete a sputtering target structure 1of the invention (FIG. 1). In this, the solder wettability of the partswas good.

The sputtering target structure 1 was used for sputtering. Thesputtering target structure 1 was stable until the sputtering target 2was consumed.

A new sputtering target was bonded to the used backing plate, and theresulting structure was used for sputtering.

After three-times repeated use of the backing plate 3, the platedeformed little, and the plate was resistant to repeated use of 20 timesor more.

Example 2

In the same manner as in Example 1, five copper pipes (their crosssection is oval, having a major diameter of 25 mm, a minor diameter of 8mm and a pipe wall thickness of 1.5 mm) were aligned in the same ironchamber as that used in Example 1. A mixed silicon carbide powder(#120/#400=3/1) was formed into a slurry with 3% silica sol in such amanner that the powder content could be 500 g/liter. The slurry was castinto the space of the iron chamber. This was dried at 120° C., and thenfired in air at 600° C., and a silicon carbide shaped article withcopper pipes built therein was thus obtained.

In the same manner as in Example 1, a copper plate was disposed on bothfaces of the shaped article. Also similarly, an aluminium melt was castinto the chamber and solidified under high pressure, and a backing platewas thus obtained, comprising a composite material of aluminium andsilicon carbide, having copper pipes built therein, and having copperplates disposed on both surfaces thereof.

The linear expansion coefficient of the backing plate was 8.3×10⁻⁶/K.

Next, onto the copper plate disposed on one side of the backing plate, asolder tin was applied at 280° C. Next, a titanium sputtering target(having a thickness of 16 mm, a length of 1,900 mm and a width of 350mm) was bonded to it to complete a sputtering target structure of theinvention. In this, the solder wettability of the parts was good.

Comparative Example 1

A molybdenum sputtering target was bonded to a copper backing platehaving a thickness of 1 mm, a length of 2,000 mm and a width of 400 mm,using a solder tin, to thereby construct a sputtering target structure(with a cooling channel built therein).

This was used in sputtering, but it warped too much and therefore couldnot serve as a sputtering target.

INDUSTRIAL APPLICABILITY

In the sputtering target structure of the invention, the linearexpansion coefficient difference between the sputtering target and thebacking plate is extremely small. Accordingly, when the two members arebonded together with a solder material, they do not warp and can beformed into the intended sputtering target structure. In the invention,in addition, inexpensive tin may be used as the solder. In particular,in the sputtering system to be used in a process of producingliquid-crystal devices, the sputtering area is large. In such a system,the sputtering target structure of the invention having a small linearexpansion coefficient difference is expected to make a greatcontribution to the stabilization of the process of producingliquid-crystal devices.

1. A sputtering target structure formed by bonding a sputtering targetand a backing plate, wherein the backing plate is formed of a materialthat has a linear expansion coefficient different from that of thesputtering target material by at most 2×10⁻⁶/K, and a copper platehaving a thickness of from 0.3 to 1.5 mm is disposed on at lest one faceof the backing plate.
 2. The sputtering target structure as claimed inclaim 1, wherein the material to constitute the backing plate is acomposite material that comprises aluminium or aluminium alloy as thematrix and, as incorporated therein, one or more granular or fibrousreinforcing materials selected from the group consisting of carbon,silicon carbide, alumina, silicon nitride, mullite and aluminium borate,and the material has a linear expansion coefficient of from 3.5 to17×10⁻⁶/K.
 3. The sputtering target structure as claimed in claim 1,wherein the sputtering target and the backing plate are bonded togetherwith indium, tin or their alloy.
 4. The sputtering target structure asclaimed in claim 1, wherein the backing plate has a cooling channelinside it and the inner cooling channel is a copper or stainless steelpipe.
 5. The sputtering target structure as claimed in claim 2, whereinthe backing plate has a cooling channel inside it and the inner coolingchannel is a copper or stainless steel pipe.
 6. The sputtering targetstructure as claimed in claim 3, wherein the backing plate has a coolingchannel inside it and the inner cooling channel is a copper or stainlesssteel pipe.